This invention relates to heat exchange catheters, and particularly to catheters that exchange heat with the blood stream of a patient.
Heat exchange catheters are used in many instances for a variety of reasons. Some surgeries, for example, are better performed when the patient cools to a hypothermic state. In other instances, a patient may suffer from accidental hypothermia and may need to be warmed to a normothermic temperature e.g. 98.6xc2x0 F. Many heat exchange catheters include the capability of infusing fluids such as nutrition, medicine and contrast agents into the blood.
Post surgical patients risk infection and fever. A fever can be controlled through the use of a heat exchange system having an intravascular heat exchange catheter. One such system is disclosed in commonly assigned U.S. Pat. No. 6,146,411, issued Nov. 14, 2000 and incorporated herein by reference. This U.S. patent teaches an exemplary system used to regulate patient temperature.
The principals of heat exchange applicable to any flowing medium (including blood) dictates the amount of heat transfer. In blood, the heat transferred depends on many things including the volumetric flow rate of the blood, the geometry of the heat exchanger and the temperature difference between the heat exchanger and the blood.
Blood has a maximum desirable heating limit. Beyond about 41xc2x0 C., blood coagulates. This limits the maximum operating temperature of known intravasculature catheters. Because the operating temperature of an intravascular catheter is limited, the catheter geometry takes on an increased importance to effectuate overall heat transfer.
Commonly assigned U.S. Pat. No. 6,126,684 issued Oct. 2, 2000 is incorporated herein by reference. This teaches a heat exchange catheter having smooth tubular balloons in serial alignment to exchange heat with the blood stream of a patient. The balloons each have an exterior surface that facilitates heat exchange with flowing blood.
U.S. Pat. No. 6,096,068 teaches a heat exchange catheter having a contoured outer surface and a heat exchange core. The contoured outer surface increases heat exchange surface area as compared to smooth tubular balloons. The contoured outer surface increases heat exchange fluid turbulence and flowing blood turbulence to improve heat transfer. These effects improve the heat transfer capability of the catheter.
U.S. Pat. No. 5,657,963, particularly the description of FIG. 6, teaches a catheter having heat exchange tubes having a nominal double helix configuration. The tubes themselves are formed from nitinol, a shape memory alloy. Initially the tubes are relatively straight at room temperature and insert into the vasculature in this straight configuration. Once inserted, commencement of refrigerant flow through the nitinol tubes causes the tubes to spiral, and thereby achieve more acute double helix configuration.
One difficulty with using alloy heat exchange tubes is that the flexibility and the tubes may be insufficient to effectuate safe insertion of the catheter into the vasculature of a patient. Further, while the helix may change shape, the nominal tube diameters may not change significantly. An unnecessarily large entry hole may be cut into one of the patients"" primary blood vessels to facilitate insertion of the catheter tube into the vasculature.
What is desired is a heat exchange catheter having a geometry that is optimally designed for transferring heat to flowing blood, and which safely inserts into a patient.